W11: Invertebrate Physiology (Insects & Elevated CO2) [Dr. Blair]

Question 1

Insects & Elevated CO2?

Answer 1

As CO2 levels increase from 300ppm to 420ppm, there have been physiological implications for all life on Earth.

Question 2

Direct effects of elevated CO2 on insects? (3)

Answer 2

• Mostly minimal.
• No respiratory implications.
• To succumb to toxic effects, CO2 levels would have to reach ~40 000ppm.

Question 3

Indirect effects of elevated CO2 for insects? (5)

Answer 3

• Major concern, as it’s causing,
• High mortality.
• Decreased reproduction.
• Decreased development.
• Decreased survival.

Question 4

What kind of insects do elevated CO2 greatly affect?

Answer 4

Phytophagous insects.

Question 5

Phytophagous insect attributes? (2)

Answer 5

• Major group of more than 500 000 species.
• All plants have at least 1 phytophagous insect species.

Question 6

What are the two major nutrients in plants? (2)

Answer 6

• Carbon (from Carbohydrates).
• Nitrogen (from Proteins).

Question 7

Plant-Insect implications? (2)

Answer 7

• Elevated CO2 causes an increase in C & a decrease in N in plants. This is beneficial for plants but causes the dilution effect (increase in C:N ratio).
• Having less N means that insects are getting less nutrition, therefore elevated CO2 causes insects to have nutritional stress but they have strategies.

Question 8

Strategies used by insects to combat nutritional stress caused by elevated CO2? (2)

Answer 8

• Compensatory feeding.
• Increasing midgut length.

Question 9

Compensatory feeding?

Answer 9

= when insects increase their food intake to compensate for reduced nutrient quality in plants.

Question 10

Types of insect herbivores? (5)

Answer 10

• Leaf chewers.
• Phloem feeders.
• Leaf miners.
• Root feeders.
• Gallers.

Question 11

Leaf chewers & elevated CO2 attributes? (5)

Answer 11

• Most leaf-feeding species.
• Have chewy mouthparts.
• Feed on leaf tissue.
• Increased compensatory feeding but,
• Decreased development, size & fecundity.

Question 12

Egs of leaf chewers? (3)

Answer 12

• Grasshoppers.
• Caterpillars.
• Locusts.

Question 13

An exception to leaf chewers?

Answer 13

Locusts & elevated CO2.

Question 14

Locusts & Elevated CO2 attributes? (3)

Answer 14

• Carbohydrate limited.
• Increased C:N ratios promote locust outbreaks (locust population booms).
• Locust population booms are a problem to agriculture, farmers.

Question 15

Phloem feeders attributes? (5)

Answer 15

• Suck on sap.
• Most sap-sucking species.
• Mixed responses.
• Some are compensatory feeders.
• Certain aphid species benefit/thrive well as they benefit from high C content plants (extra sugars).

Question 16

Eg of Phloem feeders?

Answer 16

Aphids.

Question 17

Leaf miners attributes? (3)

Answer 17

• Eat the internal structure of leaves.
• Less well studied.
• Decreased development, size & fecundity (due to nutrient dilution in leaf tissue).

Question 18

Eg of Leaf-mining insects?

Answer 18

Leaf miner moths.

Question 19

Root feeders attributes? (3)

Answer 19

• Less well studied.
• Much less N in roots.
• Decreased development & survival (due to nutrient dilution in roots).

Question 20

Eg of Root feeding insects?

Answer 20

Wireworms.

Question 21

Gallers attributes? (3)

Answer 21

• Highly specialised to have a relationship with certain species.
• Less well studied.
• Variable responses.

Question 22

Eg of Gallers?

Answer 22

Gall wasps.

Question 23

How can an insect be more efficient at getting nitrogen from food?

Answer 23

Insects that feed on low nitrogen diets increase their midgut length in order to maximise nutrient absorption (gives food more time to digest/absorb).

Question 24

Egs of insects that have increased their midgut length? (2)

Answer 24

• Lepidoptera (Caterpillars).
• Orthoptera (Grasshoppers).

Question 25

Midgut changes in Lepidoptera (Caterpillars)? (2)

Answer 25

• Increased midgut length.
• Maximised absorption.

Question 26

Midgut changes in Orthoptera (Grasshoppers)? (2)

Answer 26

• Increased midgut length & size.
• Maximised absorption.-

Question 27

What’s the general trend with elevated CO2?

Answer 27

Decrease in insect size.

Question 28

What happens when Carbon is added to plants (via elevated CO2)? (3)

Answer 28

• Dilution effect.
• Structural effect.
• Metabolite effect.

Question 29

Dilution effect?

Answer 29

= where an increase in one component (carbon in plants) dilutes the concentration of another (nitrogen in plants), reducing the overall nutritional quality of plants.

Question 30

Structural effect?

Answer 30

= where the increase in carbon in plants causes plants to be tougher to forage on.

Question 31

Result of the Dilution effect & Structural effect?

Answer 31

Insects should now increase their feeding time & foraging time, which may result in trade-offs.

Question 32

How do insects then adapt to the Structural effect?

Answer 32

Insects such as locusts change their foreguts by increasing their crop/gizzard size (to reduce the time spent eating more food). Therefore, they respond to more dignified grass.

Question 33

Metabolite effect?

Answer 33

= where plants are increasing their phenolic compounds & tannins as CO2 levels increase.

Question 34

Result of the Metabolite effect? (3)

Answer 34

• Plants are getting more defences.
• Plants are being less palatable.
• Intereferes with digestion of insect herbivores (makes plants harder to digest).

Question 35

Eg of Metabolite effect in insects?

Answer 35

Seen in elevated CO2 & caterpillars, where the increased phenolic concentration in plants deters generalist insect herbivores.

Question 36

Who can deal with increased plant defences better between specialists & generalists?

Answer 36

Specialists.

Question 37

Why can specialists deal with increased plant defences better than generalists?

Answer 37

It’s because increased phenolic concentration benefits specialists, who have specialised digestive systems that make them more resilient.

Question 38

Why can’t generalists deal with increased plant defences like specialists?

Answer 38

It’s because increased phenolic concentration causes decreased development, size & fecundity, making them more susceptible to plant defences.

Question 39

Plant-Insect implications? (3)

Answer 39

• Dilution effect (High C:N ratios; Lower quality).
• Structural effect (Increased plant structure; Harder to eat).
• Metabolite effect (Increased metabolites; Harder to digest).

Question 40

Way insect herbivores adapt to Dilution effect?

Answer 40

Compensatory feeding (generalists).

Question 41

Way insect herbivores adapt to Structural effect?

Answer 41

Compensatory feeding (generalists).

Question 42

Way insect herbivores adapt to Metabolite effect?

Answer 42

Feeding, but specific to specialists.

Question 43

General implications of elevated CO2 on phytophagous insects? (4)

Answer 43

• Slowed growth due to increased C:N ratio.
• Prolonged development due to increased C:N ratio.
• Slow digestion due to increased C:N ratio & increased metabolites.
• Decreased fecundity/reproduction due to decreased body size & poor nutrition.

Question 44

Super summary? (3)

Answer 44

• The basics (insects are poikilothermic; minimal direct effects; major indirect effects).
• Elevated CO2 & Insects (influence on plants; C:N ratios; structure; metabolites).
• General trends (elevated CO2; development; metabolism; reporduction).